The liquid skin cleanser market is growing at a rapid rate. These products became popular originally because of their convenience, reduced mess at the sink and implied improved hygiene compared to bar soaps. Most formulas were based on soap because it is inexpensive. There was later a move to add antibacterial ingredients to add value to the category and ultimately increase market share. Most recent attempts at value added features are to provide mildness and skin after-feel without sacrificing luxurious lather associated with soap-based formulas. The use of glycerin, sorbitol, vitamin E, coco fatty acid derivatives/salts, alkyl quaternary salts, sugar esters and the like are used to support foam stability and provide skin after-feel. Such additives are well known in the art. Many of these additives are either expensive, compromise lather quality or add tackiness during or after the drying stage after use. Unfortunately also, the soap-based formula has not been upgraded along with the additive features, presumably because of the added cost associated with the skin care additives.
U.S. Pat. No. 5,057,311, issued to the Kao Corporation, relates to the combination of an alkyl saccharide type surfactant and a cationic polymer to impart mildness and after feel to skin and hair. It is well known in the art that cationic materials have an affinity to skin and that saccharides (sugars) impart mildness. Kao has synthesized chemical structures that possess the required chemical moieties to achieve the intended results. On the other hand, the patentees do not teach or anticipate the use of ethylene oxide--propylene oxide--ethylene oxide (EO/PO/EO) tri-block copolymer surfactants in combination with polyvinylpyrrolidone (PVP). In fact, such tri-block copolymer surfactants are notorious for their low foam character and are used in other applications for just this reason. Nonionic EO/PO/EO tri-block copolymers make excellent additives for pesticide formulations, automatic dishwashing detergents, and floor cleaners, etc. It is therefore unexpected for these copolymer surfactants to find utility in liquid skin cleansers, for which the consumer demands rich, luxurious lather.
It has now been found that the combination of nonionic EO/PO/EO tri-block copolymers together with the polyvinylpyrrolidone improves not only the foam character of liquid skin cleansers, but also the hand feel and mildness characteristics as well.